The size of the supposed heist, and its dollar value, shrank considerably last year. Some 200,000 coins turned up in an old-format bitcoin wallet last March, bringing the tally to 650,000. At the current bitcoin price of $277, which is about half of what it was a year ago, the missing coins are worth about $180 million.

But there's still no explanation of what happened to them, and no clear record of what happened on the exchange. An anonymous report last year by a bitcoin researcher, based on leaked trading logs, chronicles the activities of trading bots that apparently ran amuck in the MtGox system, indicating massive fraudulent trading.

Tokyo-based bitcoin security firm WizSec issued a report last month that supports some of the findings of the anonymous study, concluding that a bot dubbed Willy operated over several trading accounts and was able to trade at times when the exchange was not available to other users. But the WizSec report, which was cautious about not jeopardizing other investigations, said more study of Willy is needed to understand its purpose.

MtGox CEO Mark Karpeles, who bowed in ritual apology during his bankruptcy news conference at the Tokyo Stock Exchange, maintains that online thieves are to blame. He has also hinted that they may have had insider help.

In January, Japan's Yomiuri Shimbun newspaper, citing sources close to a Tokyo police probe of the MtGox collapse, reported that only 7,000 of the coins appear to have been taken by hackers, with the remainder stolen through a series of fraudulent transactions.

Karpeles said he is "mostly kept in the dark" about the ongoing police investigation and couldn't comment on it.

"I really hope we will see some kind of progress -- if possible by catching the hackers and whoever might have been helping them," Karpeles said via email. "This whole thing has been impacting a lot of people, and continuing to impact them for way too long."

Observers had doubted that the Tokyo Metropolitan Police had the resources or know-how to track the coins, and it was not surprising that last November, Bitcoin exchange Kraken was enlisted to help investigate the missing bitcoins as part of the liquidation of MtGox.

"Kraken is helping with the claims process, including evaluating the assets owed to creditors and assisting in the investigation of MtGoxs collapse," Kraken CEO Jesse Powell said via email, adding that he had no new information about what Kraken has done in the case over the past three months.

A Swiss study last year cast doubt on the theory floated by MtGox that a large volume of bitcoins could have been stolen from the exchange using so-called transaction malleability attacks.

Another key person who would be best informed about the investigation and the whereabouts of the coins is also keeping mum. Lawyer Nobuaki Kobayashi, the court-appointed trustee overseeing the liquidation of MtGox, refused a request for more information, saying he won't discuss the matter with news media. Kobayashi has also enlisted accounting firms to aid the investigation and has said missing customer transaction data is impeding progress.

Kobayashi's periodic updates on the MtGox website and meetings to inform former MtGox customers who lost bitcoin in the fiasco haven't been well received by some investors. Former MtGox protestor Kolin Burges described the November creditors' meeting on his blog thus: "Secrecy is sprinkled over everything like an artificial sweetener to hide things we're not going to like, cover up poor progress, avoid answering awkward questions, etc."

Creditors are still waiting for Kobayashi to launch a process to receive claims related to lost coins. Their next meeting is April 22.

"Although Gox certainly had a negative impact on bitcoin's brand in the short-term, the tech and currency have never been healthier," bitcoin journalist Ryan Selkis, who posted the leaked "Crisis Strategy Draft" document that outlined the missing bitcoins days before MtGox went bust, said via email.

"International exchange infrastructure, security solutions, and regulatory frameworks have all progressed dramatically -- basics you need to have in place before killer apps like remittances and enterprise-grade e-commerce are even possible."

As for Karpeles, he lost another company to bankruptcy in January -- this time MtGox parent firm Tibanne. Following a dispute with Kobayashi about money that Tibanne had apparently borrowed from the bitcoin exchange, the Tokyo District Court approved bankruptcy proceedings for Tibanne, a small Web hosting and services provider.

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